Fuel cell systems have been proposed for use as a vehicular power plant to replace the internal combustion engine, as well as for use in portable and stationary distributed electrical power generation applications. Such systems typically include a proton exchange membrane (PEM-type) fuel cell in which hydrogen is supplied as the fuel to the anode and oxygen is supplied as the oxidant to the cathode of the fuel cell. PEM-type fuel cells include a membrane electrode assembly (MEA) comprising a thin, proton transmissive, non-electrically conductive solid polymer electrolyte membrane having the anode catalyst on one of its faces and the cathode catalyst on the opposite face. A plurality of individual cells are commonly arranged in series together to form a fuel cell stack.
The MEA is sandwiched between sheets of porous, gas-permeable, conductive material which press against the anode and cathode faces of the MEA and serve as (1) the primary current collectors for the anode and cathode, and (2) mechanical support for the MEA. The MEA and primary current collector are pressed between a pair of non-porous, electrically conductive metal sheets (i.e. bipolar plates) which serve as secondary current collectors for collecting the current from the primary current collectors and conducting current between adjacent cells internally of the stack. The bipolar plate contains a flow field that distributes the gaseous reactants over the surfaces of the anode and cathode. These flow fields generally include a plurality of lands which engage the primary current collector and define therebetween a plurality of flow channels through which the gaseous reactants flow between a supply manifold at one end of the channel and an exhaust manifold at the other end of the channel.
A bipolar plate assembly is formed by assembling a pair of metal sheets such that a functional flow field is formed on each side of the bipolar plate assembly. A spacer is interdisposed between the metal sheets to define an interior volume to permit coolant flow through the bipolar plate assembly. Examples of such bipolar plate assembly are described in U.S. Pat. No. 5,776,624 issued Jul. 7, 1998, and U.S. Pat. No. 6,099,984 and assigned to the assignee of the present invention.